Process of making curved mirrors.



Patented Sept. 24, IQOI'.

K c. wmEEn. PROCESS 0F MAKING GURVED MIBRBS.

(Application Bled June 12, 1900.)

(No Model.)

INVENTOR: @J a By Attorneys,

wlT'NBssEs;

UNITED STATES PATENT OFFICE.

KNUT C. WIDEEN, OF NEW YORK, N. Y.

PROCESS OF MAKING `CURVED MIRRORS.

SPECIFICATION forming-part of Letters Patent N o. 683,163, datedSeptember 24, 1901.

Original application filed April 27, 1900, Serial No. 14,638. Dividedand this application filed June 12, 1900. Serial No. 20.087. (Nospecimens.)

To @ZZ whom, it may concern:

Beit known that I, KNUT C. WIDEEN, a subject of the King of Sweden andNorway, residing in the city, county, and State of New York, haveinvented certain new and useful Improvementsin Processes of MakingCurved Mirrors, of which the following is a specification.

My invention provides a process whereby curved mirrors of greatstrength, rigidity, and regularity of curvature may be made cheaply andof unusually large size.

My invention provides also a process for making a curved mirror which isespecially suitable for use in the system for collecting and utilizingsolar heat described in my application for Letters Patent, Serial No.14, 638,

led April 27, 1900, of which the present application is a division.

It provides also various other improvements, all of which will be setforth in detail in the following specification.

In the accompanying drawings, illustrating one embodiment of myinvention, Figure l is a section of one of my concave mirrors, a similarconvex mirror being shown in dotted lines. Fig. 2 is a View similar toFig. l, but on a larger scale, and showing the process for manufacturingone of my improved mirrors. Fig. 3 is a plan of one of my improvedmirrors in its frame.

The mirror is supported at its edges and subjected at its centralportion to differing pressures of a Huid on the face and a iiuid on theback thereof, the duid at one side being preferably the atmosphere. Byvarying the difference of pressure on the opposite sides the degree anddirection of curvature are varied, and by using for one of the fluids amaterial which is subsequently hardened I obtain a sti backing, moldedon the back of the vmirror and fitting the same closely. By pressure Imean absolute pressure,whether greater or less than that of theatmosphere. For example, if the Huid-pressure on the face of themirror-that is, the atmospheric pressure-be greater than that on theback (which must therefore be the pressure of a partial vacuum, anypressure less than that of the atmosphere) the curvature is concave, butif the pressure at the back be greater than that of the atmosphere thecurvature is con- Vex.

For the purpose of cheaply constructing my system of collecting andutilizing solar heat above referred to it is obviously advantageous touse curved mirrors of considerable size. By the method herein describedI produce cheaply and expeditiously mirrors of accurately-determinedconcavity or conveXity and evenness and of considerable size-say, forexample, ten to Ytwelve feet in diameter. It is to be understood,however, that my process may be used in making smaller curved mirrors.

Referring to the drawings, D is a casing having a body portion circularin outline and depressed at the center, so as to form the segment of asphere, and having' a rim d projecting upward all around such centerportion,- forming a chamber E. The inner edge of the rim d is rabbeted,as shown at d', and carries au annular washer (Z2 of yielding material.On the outside of the rim are formed a series of perforated lugs (Z3,used in attaching the mirror to its supports or in handling the castingsin the process of manufacturing the mirror.

G is the plate of reflecting materiale-such as silvered glass,celluloid,or polished metalwhich forms the reiiector propel'. At twopoints of the casting D shown diametrically opposite, are perforationsd4 d5. My process is best carried out with the mirror and casting iu asubstantially horizontal position, as shown in Figs. 1 and 2, and theperforations d4 d5 are best placed at the highest possible points of thecasting when it is in such horizontal position.

H is a vessel of any convenient form and size, in which the mirror andcasting are to be submerged in hot water in the process of curving themirror. Connected to the orifices d4 and (Z5 are respectively anair-pump K and a vessel L for stearin, rosin, lead, or the like. Thepump K is connected by means of a tube k, having a cock 7c. The vessel Lis connected by means of a tube Z, in which is a cock Z. Under thevessel L, wherein the material which is kept molten by heat is stored,is a heater typiied by a gas-burner Z2.

The manner of carrying out my process with this apparatus is as follows:The tubes IOO /t' and l being attached to the casting and to the pump Kand the vessel L and a plane mirror being set tightly on the packing orwasher d?, the whole is immersed, as shown, in a bath of water or otherliquid in the vessel H at about 80 centigrade, where it is heateduniformly to this temperature, so as not to chill the molten backingmaterial. Both cocks 7e and Z are then opened and the air-pump K set inoperation, the stearin, rosin, or lead, when one of these materials isused, being maintained in a liquid condition by the heater. As the airis withdrawn the stearin or the like takes its place until the entirechamber E is filled. 'The connection of the air-pump being at thehighest point of the chamber possible in the position shown, when theair of the chamber is entirely exhausted and not before the air-pu mpwill suck stearin. At this point the cock l is closed and the operationof the pump continued to withdraw a portion of the [luid backing in thechamber E to form a partial vacuum therein. As the stearin is nowwithdrawn a portion of the pressure on the back of the mirror is removedand the atmosphere pressing on the face of the mirror presses the sameinwardly. The atmospheric pressure being iluid and the glass beingelastic and having a fluid backing, the effective pressure is the sameat all points and in all directions, and the mirror is bent into a truespherical shape. When the desired degree of curvature is obtained, thepump is stopped and the connection lt closed. The whole is then returnedslowly, with the bath E', Fig. 2,150 atmospheric temperature,the stearinhardening to a compact mass. It is obvious that a great variety ofmaterials may be used instead of the stearin, rosin, or lead referredto, the principal desideratum being that it shall enter the chamber E inliquid form and shall subsequently become quite hard, so as to give afirm backing to the mirror and stilfen the Whole as much as possible.Stearin is especially useful because of its slight expansion under heatand also its slight contraction in solidifying and because it melts at acomparatively low temperature,(77o centigrade,) and is about as hardwhen cold as` wood of average hardness. To avoid cracking of thestearin, where stearin is used, I cool the finished mirror very slowly.I have found a rate of lo centigrade every two minutes satisfactory.

It will be understood that there is a constant atmospheric pressure onone side of the glass and another duid-pressure on the inner side thelatter being greater or less than the atmospheric and beingsuch that thedierence between it and the atmospheric pressure produces the directionand degree of curvature desired. Where a concave reflector is desired,the pressure within the chamber is less than the atmospheric pressure.By means of the apparatus shown the degree of curvature is controlleddirectly by the pump K, which sucks out the fluid and with it thepressure from the chamber until the reflector is observed to have thedesired curvature.

In making a convex reflector the same apparatus may be used. In suchcase the air is drawn out of the chamber and the backing materialsubstituted therefor, as before. Then, instead of withdrawing suchmaterial, the outlet is closed and an excess of filling material forcedinto the chamber. The filling material, being in a liquid condition, ofcourse forces the reflector G', Fig. l, outward at the center, (the samebeing held down at the edges in any suitable manner,) with an equalpressure at all points and in all direc* tions,and therefore into atruesphericalshape.

Though I have described with great particularity of detail oneembodiment of my invention, yet it will be apparent that manymodifications of the same, both in the general arrangement and in theindividual features thereof,are possible to those skilled in this artwithout sacrificing all the advantages of my invention and withoutdeparting from the spirit thereof.

I do not in this application claim the iniproved mirror disclosed, thesaine being claimed in mypending application, Serial No. 27,143, filedAugust 17, 1000.

XVhat I claim, therefore, and desire to sccure by Tietters Patent, is aprocess for inaking curved mirrors having the following-defined novelfeatures, each substantially as described:

l. The process of making a curved mirror having a hard backing whichconsists in supporting a mirror at its edges, submitting said mirror todiifering pressures of a fluid on the face and a iiuid on the backthereof to curve said mirror, and then hardening the Huid on the back toform a hard backing.

2. The process of making a curved mirror having a stearin backing whichconsists in supporting a mirror at its edges, submitting said mirror tothe pressure of the atmosphere on its face, and to the pressure of fluidstearin on the back thereof, said pressures diering so as to curve saidmirror, and solidifying said stearin.

In witness whereof I have hereunto signed my naine in the presence oftwo subscribing witnesses. Y

. KNUT C. lVIDEEN. Vitnesses:

D. A. UsINA, FRED WHITE.

IOO

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